CO, HI and Star Formation in the Large Magellanic Cloud

Abstract

The Large Magellanic Cloud is an ideal laboratory for studying cloud evolution and star cluster formation. We will review CO and HI observations and compare observational signatures of star formation with the molecular and atomic gas. High-mass star formation shows good spatial correspondence with CO, and the three types, Types I, II and III of GMCs, with different star formation activity represent an evolutionary sequence from the initial inactive phase to the subsequent highly active phase in star formation. The dense clumps within GMCs show a similar evolutionary trend on smaller scales. It is likely that star formation takes place rapidly in 1–10 Myr roughly close to the free-fall timescale at 10–100 pc. GMCs are enveloped by relatively dense HI having density of 100 cm$^{-3}$. The envelope is continuously accreting onto the GMCs to increase the GMC mass with an average mass accretion rate of ∼0.1 M$_\odot$ yr$^{-1}$. The HI filaments are formed by compression due to supergiant shells as seen in active cluster formation in 30 Dor, N159, N48, etc. Recent findings of the Galactic starburst regions suggest that the active high-mass star formation is often triggered by cloud-cloud collisions which cause efficient three dimensional compression of dense gas. The interface layer in such collisions creates higher turbulent speed and higher mass-accretion rate which facilitates rapid high-mass star formation in $10^5$ yrs.